JPH06112231A - Charge transfer element and its manufacture - Google Patents

Abstract

PURPOSE:To suppress occurrence of defectives due to mask displacement, to suppress yield drop caused by short circuit between aluminum wirings and to suppress deterioration of device characteristic caused by plasma damage or thinner insulation film. CONSTITUTION:An insulation oxide film 42 is formed on a semiconductor substrate 41, and then a polycrystalline silicon 43 containing a phosphorus is formed over the entire surface of the substrate. Then with a photoresist used as a mask, reactive ion-etching is performed, so that the profile of the polycrystalline silicon is formed into a taper shape, to obtain the first electrode 45. On top of that, with the insulation film 46 in between, polycrystalline silicon is buried between the first electrodes 45, to obtain the second electrode 49. Thus, no step is formed where two electrodes overlap each other, for obtaining a flat structure with no potential barrier, so that electric charge is efficiently transferred.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge transfer device applied to, for example, a CCD imager and a manufacturing method thereof.

[0002]

2. Description of the Related Art A charge transfer element is basically a kind of dynamic analog shift register and is an element for controlling an accumulation or transfer operation of an electric charge amount as an analog signal by an electrode having a periodic structure. The CCD is also a type of charge transfer device and is used as a light receiving device in television cameras and the like.

As a structure of a conventional charge transfer element, for example, there is one as shown in FIG. FIG. 5 shows the structure as a cross section while sequentially showing the manufacturing process of the charge transfer device. In FIG. 5, 1 is a semiconductor substrate, 2 is an insulating film,
3 is phosphorus-containing polycrystalline silicon. First, FIG.
As shown in FIG. 5A, a photoresist 4 is formed on the upper surface of the phosphorus-containing polycrystalline silicon 3, and then, as shown in FIG. 5B, the photoresist 4 is used as a mask for reactive ion etching or the like. The contained polycrystalline silicon 3 is selectively removed to form the first electrode 5. Further, the insulating film 6 is formed on the surface of the first electrode 5.

Then, as shown in FIG. 5C, the insulating film 6 is formed.
After growing the phosphorus-containing polycrystalline silicon 7 over the entire upper surface of the photoresist, a photoresist 8 is formed in the electrode formation portion (see FIG. 5D). Next, as shown in FIG. 5E, the phosphorus-containing polycrystalline silicon 7 is selectively removed by reactive ion etching or the like using the photoresist 8 as a mask to form a second electrode 9, and further, a first electrode. An insulating film 10 is formed on the surface of 9.

Next, as an application of the charge transfer device manufactured according to the above process to a device, a CCD shown in FIG.
There is an imager. 6 (a) and 6 (b) are plan views showing a simple manufacturing process and structure of a sensor forming portion in a conventional CCD imager, and FIGS. 6 (a ') and 6 (b'). Are respectively shown in FIG. 6 (a) and FIG. 6 (b).
3 is a cross-sectional view taken along the line AA ′ and a cross-sectional view taken along the line BB ′ in FIG.

First, an insulating oxide film 22 is formed on a semiconductor substrate 21 as shown in FIGS.
After growing the phosphorus-containing polycrystalline silicon, a photoresist is formed on the upper surface thereof, and the phosphorus-containing polycrystalline silicon is selectively removed by reactive ion etching using this as a mask to form the first electrode 23. Further, a silicon oxide film (insulating film) 24 is formed on the surface of the first electrode 23.

Next, as shown in FIGS. 6 (b) and 6 (b '), phosphorus-containing polycrystalline silicon is grown over the entire surface of the silicon oxide film 24, and then the selectively formed photoresist is used as a mask for reactivity. The phosphorus-containing polycrystalline silicon is removed by ion etching or the like to form the second electrode 31, and the silicon oxide film (insulating film) 32 is further formed on the surface of the second electrode 31 to complete the process. As a result, 3 in the figure
3 is a sensor forming part.

Then, a signal charge is generated by the light incident on the sensor forming portion 33, and this charge is transferred by driving the first electrode 23 and the second electrode 31 as a transfer electrode at a predetermined clock, and is transferred to the image pickup device. Used as.

[0009]

By the way, in the manufacturing process of the charge transfer device, since a highly accurate mask alignment is required when forming the above-mentioned second electrode, a defective product is generated due to the mask displacement. There was a problem that it was easy to do.

Further, there is the following problem due to the step difference due to the overlap of the first electrode and the second electrode. In the conventional structure, when etching off the upper film of aluminum (Al) or the like, an etching residue of aluminum is likely to occur in the step portion, which causes a short circuit between the aluminum wirings, and the yield is reduced. In order to remove this aluminum etching residue, overetching must be carried out for a long time, resulting in a new defect that plasma damage is large, and at the same time, the uppermost insulating film thickness is reduced and the device thickness is reduced. However, there is a drawback that the characteristics of No. 1 deteriorate.

On the other hand, according to the "method for manufacturing a MOS type semiconductor device" described in Japanese Patent Laid-Open No. 272067/1988, a step of forming the second electrode between the first electrodes by etching back is disclosed. Even by such a step, since the step difference of the first electrode is particularly large, the step difference when the second electrode overlaps cannot be flattened, and the above problems cannot be solved.

Therefore, according to the present invention, generation of defective products due to mask misalignment can be suppressed, reduction in yield due to short circuit between aluminum wirings can be suppressed, and deterioration of device characteristics due to plasma damage or reduction in insulating film thickness can be suppressed. An object of the present invention is to provide a charge transfer device and a manufacturing method thereof.

[0013]

In order to achieve the above object, a charge transfer device according to the present invention is formed on a semiconductor substrate and an insulating film on the semiconductor substrate, and a tapered portion is formed on a side surface thereof. A first transfer electrode, a first insulating film formed on the first transfer electrode, and a taper portion formed between the first transfer electrode and along the taper portion of the first transfer electrode. A second transfer electrode formed on the side surface thereof and a second insulating film formed on the second transfer electrode.

In a preferred embodiment, the first transfer electrode has a mountain-shaped cross section. The second transfer electrode has a cup-shaped cross section.

A method of manufacturing a charge transfer device according to the present invention comprises:
Forming a first polycrystalline polysilicon layer on a semiconductor substrate via an insulating film; selectively forming a first photoresist on an electrode portion of the first polycrystalline polysilicon layer; Etching the first polycrystalline polysilicon layer using a photoresist as a mask to form a first transfer electrode having a tapered portion on a side surface thereof;
A step of forming a second polycrystalline polysilicon layer on the transfer electrode and the insulating film, and a step of forming a second photoresist on the second polycrystalline polysilicon layer so as to have a flat surface. Etching the second photoresist and the second polycrystalline polysilicon layer at a constant rate to form a second transfer electrode having a taper portion on a side surface between the first transfer electrodes. And

[0016]

In the present invention, the first polycrystalline polysilicon layer is formed in a tapered or stepwise cross-sectional shape to form the first transfer electrode, and the insulating film is formed on the first transfer electrode. A second transfer electrode is formed by filling the polysilicon layer between the first electrodes. As a result, the two transfer electrodes have a flat structure having no step in the overlapping portion, and the signal charges can be transferred.

Therefore, highly accurate mask alignment is not required at the time of forming the second transfer electrodes, and the generation of defective products due to mask misalignment is suppressed. Further, since there is no step due to the first and second transfer electrodes, a short circuit due to an etching residue of aluminum that occurs during the etching off process of the upper film formation of aluminum or the like is reduced, and the yield is improved. further,
Overetching can be reduced, and deterioration of device characteristics due to plasma damage or reduction of the uppermost insulating film thickness can be suppressed.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a method of manufacturing a charge transfer device according to the present invention. First, an insulating oxide film 42 is formed on a semiconductor substrate 41 as shown in FIG.
Polycrystalline silicon containing phosphorus (corresponding to a first polycrystalline silicon layer) 43 is formed on the entire surface of the substrate. Then first
A photoresist (corresponding to the first photoresist) 44 is selectively formed on the upper surface of the phosphorus-containing polycrystalline silicon 43 in order to form a region to be an electrode.

Next, as shown in FIG. 1 (b), the phosphorus-containing polycrystalline silicon 4 is formed under appropriate etching conditions such as reactive ion etching using the photoresist 4 as a mask.
3 is selectively removed to form a tapered first electrode (corresponding to the first transfer electrode) 45. Then, the entire surface of the substrate is processed in an oxidizing atmosphere to form a silicon oxide film (corresponding to a first insulating film) 46 on the surface of the first electrode 45.

Then, as shown in FIG. 1C, after phosphorus-containing polycrystalline silicon (corresponding to the second polycrystalline polysilicon layer) 47 is grown on the entire surface of the substrate, a photoresist (second photoresist) is used. 48) is formed on the entire surface of the substrate so that the surface becomes flat. Then, FIG. 1 (d)
As shown in FIG. 5, the second electrode is formed by etching the entire surface of the substrate with the photoresist 48 and the phosphorus-containing polycrystalline silicon 47 under the etching conditions such that the etching rates are equal, that is, the selection ratio is “1”. 49 (corresponding to a second transfer electrode) is formed between each first electrode 45. Here, the second electrode 49 has a tapered portion along the tapered portion of the first electrode 45 on its side surface. After that, the entire surface of the substrate is processed in an oxidizing atmosphere, a silicon oxide film (corresponding to a second insulating film) 50 is formed on the surface of the second electrode 49, and the process is completed.

In the charge transfer device manufactured by the above manufacturing process, the phosphorus-containing polycrystalline silicon has a tapered cross-sectional shape to form the first electrode 45, and the insulating film (silicon oxide film) 46 is formed on the first electrode 45. The second electrode 49 has a structure in which phosphorus-containing polycrystalline silicon is embedded between the first electrodes 45. Therefore, the two electrodes have no step in the overlapping portion, that is, it is possible to transfer charges with a flattened structure. Specifically, the first
The electrodes 45 and the second electrodes 49 are driven by a predetermined clock using the transfer electrodes. In this case, the first and second electrodes 45,
Since the overlapping portion of 49 is flattened, the potential barrier between the first and second electrodes 45, 49 can be removed. Therefore, the charges are efficiently transferred by applying an appropriate clock voltage.
As a result, the following effects can be obtained.

In the manufacturing process, highly accurate mask alignment is not required when forming the second electrode 49, and the production of defective products due to mask misalignment can be suppressed to improve the yield. Since the overlapping portions of the first electrode 45 and the second electrode 49 are flattened, there is no step even when etching off the upper film formation of aluminum (Al) or the like. The rest is less likely to occur,
Therefore, a short circuit between aluminum wirings is suppressed, and the yield is improved.

On the other hand, when performing over-etching to remove the aluminum etching residue,
The time is short, and therefore plasma damage is also small, and it is possible to prevent a decrease in the uppermost insulating film thickness and prevent deterioration of device characteristics.

Next, FIG. 2 shows a CCD imager as an application of the charge transfer device manufactured according to the above process to a device. 2A to 2C are CCDs.
FIG. 3 is a plan view showing a simple manufacturing process and structure of a sensor forming portion in an imager, and FIGS. 2 (a ′) and 2 (b ′) are respectively shown in FIGS. 2 (a) and 2 (b). It is an arrow sectional view of AA 'and an arrow sectional view of BB'.

2 (a), (a ') and FIG. 2 (b),
The structure shown in (b ') is manufactured by the same process as the manufacturing process shown in FIGS. However, the silicon oxide film on the surface of the second electrode 49 is not formed. Next, as shown in FIG. 2C, a photoresist is selectively formed in a portion that will later become a sensor forming portion, and the sensor forming portion 51 is formed by reactive ion etching or the like using this photoresist as a mask. Then, a silicon oxide film 52 is formed on the entire surface of the substrate, and the process is completed. Further, the formation portion of the wiring and the like is also formed by etching after the selective photoresist formation with the same mask. 3 (a) and 3
2B is a sectional view taken along the line CC ′ and a sectional view taken along the line DD ′ of FIG. 2C, respectively.

When a signal charge is generated by the light incident on the sensor forming portion 51, the charge is transferred by driving the first electrode 45 and the second electrode 49 as transfer electrodes at a predetermined clock. , Second electrodes 45, 49
Since the overlapping part of is flattened, the potential barrier between the first and second electrodes 45 and 49 is removed, and charges can be efficiently transferred.

Next, FIG. 4 is a diagram showing another embodiment of the present invention, which is an example in which the shape of the first electrode is changed.
First, as shown in FIG. 4A, an insulating oxide film 62 is formed on a semiconductor substrate 61, and then phosphorus-containing polycrystalline silicon (corresponding to a first polycrystalline polysilicon layer) 63 is formed on the entire surface of the substrate. . Next, a photoresist (corresponding to the first photoresist) 64 is selectively formed on the upper surface of the phosphorus-containing polycrystalline silicon 63 in order to form a region to be the first electrode later.

Next, as shown in FIG. 4B, isotropic etching such as chemical dry etching or wet etching is performed for a proper time by using the photoresist 64 as a mask, so that the phosphorus-containing polycrystalline silicon 6 is formed.
3 is formed into a mountain shape (especially Mt. Fuji shape). Then, FIG.
As shown in (c), anisotropic etching is performed by reactive ion etching or the like using the photoresist 64 as a mask. Next, as shown in FIG. 4D, the photoresist 64 is peeled off to form a mountain-shaped first electrode (corresponding to the first transfer electrode) 65. After that, the entire surface of the substrate is processed in an oxidizing atmosphere,
A silicon oxide film (corresponding to a first insulating film) 66 is formed on the surface of the first electrode 65.

Next, as shown in FIG. 4E, after phosphorus-containing polycrystalline silicon (corresponding to the second polycrystalline polysilicon layer) 67 is grown on the entire surface of the substrate, a photoresist (second photoresist) is used. 68) is formed on the entire surface of the substrate so that the surface becomes flat. Then, FIG. 4 (f)
As shown in FIG. 3, the second electrode is formed by etching the entire surface of the substrate of the photoresist 68 and the phosphorus-containing polycrystalline silicon 67 under the etching conditions such that the etching rates are equal, that is, the selection ratio is “1”. 69 (corresponding to a second transfer electrode) is formed between each first electrode 65. Here, the second electrode 69 has a tapered portion along the tapered portion of the first electrode 45 on its side surface, and in particular, the second electrode 69 has a tapered portion.
The electrode 69 has a cup-shaped cross section. After that, the entire surface of the substrate is processed in an oxidizing atmosphere, a silicon oxide film (corresponding to a second insulating film) 70 is formed on the surface of the second electrode 69, and the process is completed.

In the charge transfer device manufactured by the above manufacturing process, the phosphorus-containing polycrystalline silicon is formed into a mountain-shaped cross section to form the first electrode 65, and the insulating film (silicon oxide film) 66 is provided on the first electrode 65. First, phosphorus-containing polycrystalline silicon
The structure is such that the second electrode 69 is embedded between the electrodes 65. Therefore, as in the case of the above-described embodiment, there is no step in the overlapping portion of the two electrodes, and it is possible to transfer charges with a flattened structure, and the same effect can be obtained.

[0031]

As described above, according to the present invention,
The overlapping portion of the two transfer electrodes can have a flat structure without a step, and the potential barrier between the two transfer electrodes can be removed. Therefore, the charges can be efficiently transferred by applying an appropriate clock voltage.

As a result, it is not necessary to perform highly accurate mask alignment when forming the second transfer electrodes, and it is possible to suppress the generation of defective products due to mask misalignment. In addition, since there is no step due to the first and second transfer electrodes, a short circuit due to an etching residue of aluminum that occurs during the etch-off process of the upper film formation of aluminum or the like can be reduced and the yield can be improved. Furthermore, even when overetching is performed to remove etching residue of aluminum, the time is short (overetching can be reduced), and deterioration of device characteristics due to plasma damage or reduction of the uppermost insulating film thickness is prevented. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a manufacturing process of a charge transfer device according to the present invention.

FIG. 2 is a diagram showing a manufacturing process of a CCD imager to which a charge transfer device manufactured according to the process of the embodiment is applied.

FIG. 3 is a cross-sectional view of a CCD imager to which a charge transfer device manufactured according to the process of the example is applied.

FIG. 4 is a diagram showing another embodiment of the manufacturing process of the charge transfer device according to the present invention.

FIG. 5 is a diagram showing a manufacturing process of a conventional charge transfer device.

FIG. 6 is a diagram showing a manufacturing process of a CCD imager to which a conventional charge transfer device is applied.

[Explanation of symbols]

41, 61 Semiconductor substrate 42, 62 Insulating oxide film 43, 63 Phosphorus-containing polycrystalline silicon (first polycrystalline polysilicon layer) 44, 64 Photoresist (first photoresist) 45, 65 First electrode (first transfer electrode) ) 46, 66 silicon oxide film (first insulating film) 47, 67 phosphorus-containing polycrystalline silicon (second polycrystalline polysilicon layer) 48, 68 photoresist (second photoresist) 49, 69 second electrode (second) 2 transfer electrode) 50, 70 silicon oxide film (second insulating film) 51 sensor forming portion 52 silicon oxide film

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[Procedure amendment]

[Submission date] April 1, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Charge transfer device and method of manufacturing the same

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge transfer device applied to, for example, a CCD imager and a manufacturing method thereof.

[0002]

2. Description of the Related Art A charge transfer element is basically a kind of dynamic analog shift register and is an element for controlling an accumulation or transfer operation of an electric charge amount as an analog signal by an electrode having a periodic structure. The CCD is also a type of charge transfer device and is used as a light receiving device in television cameras and the like.

For example, the structure of a conventional charge transfer element is
IfFigure 7There is something like.Figure 7Is the charge transfer device
The structure is shown as a cross section, showing the manufacturing steps in order
Is.Figure 7, 1 is a semiconductor substrate, 2 is an insulating film,
3 is phosphorus-containing polycrystalline silicon. First,Figure 7
As shown in (a), the upper surface of the phosphorus-containing polycrystalline silicon 3
Photoresist 4 is formed on theFigure 7Shown in (b)
The photoresist 4 as a mask.
Selection of phosphorus-containing polycrystalline silicon 3 by etching
And then removed to form the first electrode 5. In addition, the first electric
An insulating film 6 is formed on the surface of the pole 5.

Then, as shown in FIG. 7C, the insulating film 6 is formed.
After the phosphorus-containing polycrystalline silicon 7 is grown over the entire upper surface of, the photoresist 8 is formed on the electrode forming portion (see FIG. 7D ). Then, as shown in FIG. 7E, the phosphorus-containing polycrystalline silicon 7 is selectively removed by reactive ion etching or the like using the photoresist 8 as a mask to form the second electrode 9, and further, the first electrode. An insulating film 10 is formed on the surface of 9.

Next, as an application of the charge transfer element manufactured according to the above process to a device, a CCD shown in FIG.
There is an imager. 8 (a) and 8 (b) are plan views showing a simple manufacturing process and structure of a sensor forming portion in a conventional CCD imager, and FIGS. 8 (a ') and 8 (b'). Are respectively shown in FIG. 8 (a) and FIG. 8 (b).
3 is a cross-sectional view taken along the line AA ′ and a cross-sectional view taken along the line BB ′ in FIG.

First, an insulating oxide film 22 is formed on a semiconductor substrate 21 as shown in FIGS.
After growing the phosphorus-containing polycrystalline silicon, a photoresist is formed on the upper surface thereof, and the phosphorus-containing polycrystalline silicon is selectively removed by reactive ion etching using this as a mask to form the first electrode 23. Further, a silicon oxide film (insulating film) 24 is formed on the surface of the first electrode 23.

Then, as shown in FIGS. 8B and 8B ', after phosphorus-containing polycrystalline silicon is grown over the entire surface of the silicon oxide film 24, the photoresist selectively formed is used as a mask for the reactivity. The phosphorus-containing polycrystalline silicon is removed by ion etching or the like to form the second electrode 31, and the silicon oxide film (insulating film) 32 is further formed on the surface of the second electrode 31 to complete the process. As a result, 3 in the figure
3 is a sensor forming part.

Then, a signal charge is generated by the light incident on the sensor forming portion 33, and this charge is transferred by driving the first electrode 23 and the second electrode 31 as a transfer electrode at a predetermined clock, and is transferred to the image pickup device. Used as.

[0009]

By the way, in the manufacturing process of the charge transfer device, since a highly accurate mask alignment is required when forming the above-mentioned second electrode, a defective product is generated due to the mask displacement. There was a problem that it was easy to do.

Further, there is the following problem due to the step difference due to the overlap of the first electrode and the second electrode. In the conventional structure, when etching off the upper film of aluminum (Al) or the like, an etching residue of aluminum is likely to occur in the step portion, which causes a short circuit between the aluminum wirings, and the yield is reduced. In order to remove this aluminum etching residue, overetching must be carried out for a long time, resulting in a new defect that plasma damage is large, and at the same time, the uppermost insulating film thickness is reduced and the device thickness is reduced. However, there is a drawback that the characteristics of No. 1 deteriorate.

On the other hand, according to the "method for manufacturing a MOS type semiconductor device" described in Japanese Patent Laid-Open No. 272067/1988, a step of forming the second electrode between the first electrodes by etching back is disclosed. Even by such a step, since the step difference of the first electrode is particularly large, the step difference when the second electrode overlaps cannot be flattened, and the above problems cannot be solved.

Therefore, according to the present invention, generation of defective products due to mask misalignment can be suppressed, reduction in yield due to short circuit between aluminum wirings can be suppressed, and deterioration of device characteristics due to plasma damage or reduction in insulating film thickness can be suppressed. An object of the present invention is to provide a charge transfer device and a manufacturing method thereof.

[0013]

In order to achieve the above object, a charge transfer device according to the present invention is formed on a semiconductor substrate and an insulating film on the semiconductor substrate, and a tapered portion is formed on a side surface thereof. A first transfer electrode, a first insulating film formed on the first transfer electrode, and a taper portion formed between the first transfer electrode and along the taper portion of the first transfer electrode. A second transfer electrode formed on the side surface thereof and a second insulating film formed on the second transfer electrode.

In a preferred embodiment, the first transfer electrode has a mountain-shaped cross section. The second transfer electrode has a cup-shaped cross section.

A method of manufacturing a charge transfer device according to the present invention comprises:
Forming a first polycrystalline polysilicon layer on a semiconductor substrate via an insulating film; selectively forming a first photoresist on an electrode portion of the first polycrystalline polysilicon layer; Etching the first polycrystalline polysilicon layer using a photoresist as a mask to form a first transfer electrode having a tapered portion on a side surface thereof;
A step of forming a second polycrystalline polysilicon layer on the transfer electrode and the insulating film, and a step of forming a second photoresist on the second polycrystalline polysilicon layer so as to have a flat surface. Etching the second photoresist and the second polycrystalline polysilicon layer at a constant rate to form a second transfer electrode having a taper portion on a side surface between the first transfer electrodes. And

[0016]

In the present invention, the first polycrystalline polysilicon layer is formed in a tapered or stepwise cross-sectional shape to form the first transfer electrode, and the insulating film is formed on the first transfer electrode. A second transfer electrode is formed by filling the polysilicon layer between the first electrodes. As a result, the two transfer electrodes have a flat structure having no step in the overlapping portion, and the signal charges can be transferred.

Therefore, highly accurate mask alignment is not required at the time of forming the second transfer electrodes, and the generation of defective products due to mask misalignment is suppressed. Further, since there is no step due to the first and second transfer electrodes, a short circuit due to an etching residue of aluminum that occurs during the etching off process of the upper film formation of aluminum or the like is reduced, and the yield is improved. further,
Overetching can be reduced, and deterioration of device characteristics due to plasma damage or reduction of the uppermost insulating film thickness can be suppressed.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a method of manufacturing a charge transfer device according to the present invention. First, an insulating oxide film 42 is formed on a semiconductor substrate 41 as shown in FIG.
Polycrystalline silicon containing phosphorus (corresponding to a first polycrystalline silicon layer) 43 is formed on the entire surface of the substrate. Then first
A photoresist (corresponding to the first photoresist) 44 is selectively formed on the upper surface of the phosphorus-containing polycrystalline silicon 43 in order to form a region to be an electrode.

Next, as shown in FIG. 1 (b), the phosphorus-containing polycrystalline silicon 4 is formed under appropriate etching conditions such as reactive ion etching using the photoresist 4 as a mask.
3 is selectively removed to form a tapered first electrode (corresponding to the first transfer electrode) 45. Then, the entire surface of the substrate is processed in an oxidizing atmosphere to form a silicon oxide film (corresponding to a first insulating film) 46 on the surface of the first electrode 45.

Then, as shown in FIG. 1C, after phosphorus-containing polycrystalline silicon (corresponding to the second polycrystalline polysilicon layer) 47 is grown on the entire surface of the substrate, a photoresist (second photoresist) is used. 48) is formed on the entire surface of the substrate so that the surface becomes flat. Then, FIG. 1 (d)
As shown in FIG. 5, the second electrode is formed by etching the entire surface of the substrate with the photoresist 48 and the phosphorus-containing polycrystalline silicon 47 under the etching conditions such that the etching rates are equal, that is, the selection ratio is “1”. 49 (corresponding to a second transfer electrode) is formed between each first electrode 45. Here, the second electrode 49 has a tapered portion along the tapered portion of the first electrode 45 on its side surface. After that, the entire surface of the substrate is processed in an oxidizing atmosphere, a silicon oxide film (corresponding to a second insulating film) 50 is formed on the surface of the second electrode 49, and the process is completed.

In the charge transfer device manufactured by the above manufacturing process, the phosphorus-containing polycrystalline silicon has a tapered cross-sectional shape to form the first electrode 45, and the insulating film (silicon oxide film) 46 is formed on the first electrode 45. The second electrode 49 has a structure in which phosphorus-containing polycrystalline silicon is embedded between the first electrodes 45. Therefore, the two electrodes have no step in the overlapping portion, that is, it is possible to transfer charges with a flattened structure. Specifically, the first
The electrodes 45 and the second electrodes 49 are driven by a predetermined clock using the transfer electrodes. In this case, the first and second electrodes 45,
Since the overlapping portion of 49 is flattened, the potential barrier between the first and second electrodes 45, 49 can be removed. Therefore, the charges are efficiently transferred by applying an appropriate clock voltage.
As a result, the following effects can be obtained.

In the manufacturing process, highly accurate mask alignment is not required when forming the second electrode 49, and the production of defective products due to mask misalignment can be suppressed to improve the yield. Since the overlapping portions of the first electrode 45 and the second electrode 49 are flattened, there is no step even when etching off the upper film formation of aluminum (Al) or the like. The rest is less likely to occur,
Therefore, a short circuit between aluminum wirings is suppressed, and the yield is improved.

On the other hand, when performing over-etching to remove the aluminum etching residue,
The time is short, and therefore plasma damage is also small, and it is possible to prevent a decrease in the uppermost insulating film thickness and prevent deterioration of device characteristics.

Next, FIGS. 2 and 3 show a CCD as a device application of the charge transfer device manufactured according to the above process .
It shows an imager. 2 (a) , (b),
FIG. 3C is a plan view showing a simple manufacturing process and structure of the sensor forming portion in the CCD imager, and FIGS. 2A ′ and 2B ′ are respectively FIG.
FIG. 3A is a sectional view taken along the line AA ′ in FIG. 2B and a sectional view taken along the line BB ′ in FIG.

2 (a), (a ') and FIG. 2 (b),
The structure shown in (b ') is the same as that shown in FIGS. 1 (a) to 1 (d).
It is manufactured by the same process as the process. However, the second electrode
The silicon oxide film on the surface of 49 is not formed. ThenFigure
ThreeAs shown in (c),
A photoresist is selectively formed, and this photoresist is
With the mask as a mask by reactive ion etching, etc.
The forming portion 51 is formed. Then, the entire surface of the substrate is
Then, the oxide film 52 is formed and the process is completed. Also, formation of wiring etc.
After the selective photoresist formation with the same mask
It is formed by etching.Figure 4(A) andFigure 4
(B) is respectivelyFigure 3View of C-C 'in (c)
It is a sectional view and a sectional view taken along the line D-D '.

When a signal charge is generated by the light incident on the sensor forming portion 51, the charge is transferred by driving the first electrode 45 and the second electrode 49 as transfer electrodes at a predetermined clock. , Second electrodes 45, 49
Since the overlapping part of is flattened, the potential barrier between the first and second electrodes 45 and 49 is removed, and charges can be efficiently transferred.

Next, FIG. 5 is a diagram showing another embodiment of the present invention, which is an example in which the shape of the first electrode is changed.
First, as shown in FIG. 5A , an insulating oxide film 62 is formed on a semiconductor substrate 61, and then phosphorus-containing polycrystalline silicon (corresponding to a first polycrystalline polysilicon layer) 63 is formed on the entire surface of the substrate. . Next, a photoresist (corresponding to the first photoresist) 64 is selectively formed on the upper surface of the phosphorus-containing polycrystalline silicon 63 in order to form a region to be the first electrode later.

Next, as shown in FIG. 5B, isotropic etching such as chemical dry etching or wet etching is performed for a proper time by using the photoresist 64 as a mask, and the phosphorus-containing polycrystalline silicon 6 is then removed.
3 is formed into a mountain shape (especially Mt. Fuji shape). Then, FIG.
As shown in (c), anisotropic etching is performed by reactive ion etching or the like using the photoresist 64 as a mask. Next, as shown in FIG. 5D , the photoresist 64 is peeled off to form a mountain-shaped first electrode (corresponding to the first transfer electrode) 65. After that, the entire surface of the substrate is processed in an oxidizing atmosphere,
A silicon oxide film (corresponding to a first insulating film) 66 is formed on the surface of the first electrode 65.

Next, as shown in FIG. 6E, after phosphorus-containing polycrystalline silicon (corresponding to a second polycrystalline polysilicon layer) 67 is grown on the entire surface of the substrate, a photoresist (second photoresist) is used. 68) is formed on the entire surface of the substrate so that the surface becomes flat. Then, FIG. 6 (f)
As shown in FIG. 3, the second electrode is formed by etching the entire surface of the substrate of the photoresist 68 and the phosphorus-containing polycrystalline silicon 67 under the etching conditions such that the etching rates are equal, that is, the selection ratio is “1”. 69 (corresponding to a second transfer electrode) is formed between each first electrode 65. Here, the second electrode 69 has a tapered portion along the tapered portion of the first electrode 45 on its side surface, and in particular, the second electrode 69 has a tapered portion.
The electrode 69 has a cup-shaped cross section. After that, the entire surface of the substrate is processed in an oxidizing atmosphere, a silicon oxide film (corresponding to a second insulating film) 70 is formed on the surface of the second electrode 69, and the process is completed.

In the charge transfer device manufactured by the above manufacturing process, the phosphorus-containing polycrystalline silicon is formed into a mountain-shaped cross section to form the first electrode 65, and the insulating film (silicon oxide film) 66 is provided on the first electrode 65. First, phosphorus-containing polycrystalline silicon
The structure is such that the second electrode 69 is embedded between the electrodes 65. Therefore, as in the case of the above-described embodiment, there is no step in the overlapping portion of the two electrodes, and it is possible to transfer charges with a flattened structure, and the same effect can be obtained.

[0031]

As described above, according to the present invention,
The overlapping portion of the two transfer electrodes can have a flat structure without a step, and the potential barrier between the two transfer electrodes can be removed. Therefore, the charges can be efficiently transferred by applying an appropriate clock voltage.

As a result, it is not necessary to perform highly accurate mask alignment when forming the second transfer electrodes, and it is possible to suppress the generation of defective products due to mask misalignment. In addition, since there is no step due to the first and second transfer electrodes, a short circuit due to an etching residue of aluminum that occurs during the etch-off process of the upper film formation of aluminum or the like can be reduced and the yield can be improved. Furthermore, even when overetching is performed to remove etching residue of aluminum, the time is short (overetching can be reduced), and deterioration of device characteristics due to plasma damage or reduction of the uppermost insulating film thickness is prevented. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a manufacturing process of a charge transfer device according to the present invention.

FIG. 2 is a diagram showing a part of a manufacturing process of a CCD imager to which a charge transfer device manufactured according to the process of the embodiment is applied.

FIG. 3 is a charge transfer element manufactured according to the process of the embodiment .
Shows a part of the manufacturing process of a CCD imager using a child
It is a figure.

FIG. 4 is a cross-sectional view of a CCD imager to which a charge transfer device manufactured according to the process of the example is applied.

FIG. 5 is a diagram showing a part of another embodiment of the process of manufacturing the charge transfer device according to the present invention.

FIG. 6 is another example of the manufacturing process of the charge transfer device according to the present invention .
It is a figure which shows a part of Example.

FIG. 7 is a diagram showing a manufacturing process of a conventional charge transfer device.

FIG. 8 is a diagram showing a manufacturing process of a CCD imager to which a conventional charge transfer device is applied.

[Description of Reference Signs] 41, 61 Semiconductor substrate 42, 62 Insulating oxide film 43, 63 Phosphorus-containing polycrystalline silicon (first polycrystalline polysilicon layer) 44, 64 Photoresist (first photoresist) 45, 65 First electrode (First transfer electrode) 46, 66 Silicon oxide film (first insulating film) 47, 67 Phosphorus-containing polycrystalline silicon (second polycrystalline polysilicon layer) 48, 68 Photoresist (second photoresist) 49, 69 Second electrode (second transfer electrode) 50, 70 Silicon oxide film (second insulating film) 51 Sensor forming portion 52 Silicon oxide film

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Claims (4)

[Claims] 1. A semiconductor substrate, a first transfer electrode formed on the semiconductor substrate via an insulating film and having a tapered portion on its side surface, and a first transfer electrode formed on the first transfer electrode. A second transfer electrode that is formed between the first transfer electrode and the first transfer electrode and has a taper portion along the taper portion of the first transfer electrode on its side surface; and on the second transfer electrode. A formed second insulating film, and a charge transfer device comprising: 2. The charge transfer device according to claim 1, wherein the first transfer electrode has a mountain-shaped cross section. 3. The charge transfer device according to claim 2, wherein the second transfer electrode has a cup-shaped cross section. 4. A step of forming a first polysilicon layer on a semiconductor substrate with an insulating film interposed therebetween, and a step of selectively forming a first photoresist on an electrode portion of the first polysilicon layer. And a step of etching the first polycrystalline polysilicon layer using the first photoresist as a mask to form a first transfer electrode having a tapered portion on its side surface, the first transfer electrode and the insulating film. A step of forming a second polycrystalline polysilicon layer thereon, a step of forming a second photoresist on the second polycrystalline polysilicon layer so that its surface is flat, and a step of forming the second photoresist and The second polycrystal polysilicon layer is etched at a constant rate to form a gap between the first transfer electrodes,
And a step of forming a second transfer electrode having a taper portion on its side surface.